How to Extend Parts Cleaner Solution Life
Coventya’s Greg Terrell says there are simple techniques that can be used every day in any plating shop to better characterize not only the effectiveness of the cleaners, but help determine the cleaner life that fits the process line.
Q: When is the best time to replace a cleaner on the plating line?
A: In many plating job shop or captive finishing operations, surface preparation deficiencies account for the majority of defects that result in some level of poor quality. Resulting appearance, adhesion and other aspects of poor performance occur as a result of not paying attention to the surface preparation portion of the process. True, it’s easier to see the defect after plating has occurred, although this may imply to many that the plating solution created the defect. However, many years of experience and countless hours of defect analysis (including SEM analysis methods) continue to support the significance of paying attention to the preparation cycle details — making it just as important as the plating tank itself in the overall success of the process.
Unfortunately, there are few simple, direct methods for determining when to replace a cleaner on the plating line. Aspects of every line are different. The soils, the tank loading, filtration, cleaner type, formulation, water hardness, rinsing tanks’ effectiveness and more are all known to impact cleaner life. So what’s the best way to achieve better control of your cleaning system?
Most cleaners are analyzed by a simple acid-strong base titration using a phenolphthalein indicator. This measures free alkalinity and seems to be the universal way suppliers tell customers to control their cleaning technology. Unfortunately, this doesn’t tell much about what is really going on with any particular soak or electro-cleaner solution. There is a lot of missing or misleading information in this titration alone. Cleaner life is often determined in each shop after a load of poor quality parts are produced, thereby causing costly rework and lost production time and, in worse cases, parts that must be scrapped. This proposition becomes more costly than the price of the cleaners themselves.
However, there are simple techniques that can be used every day in any plating shop to better characterize not only the effectiveness of the cleaners but also help determine the cleaner life that fits the process line.
What follows are some simple guides and analytical techniques for helping to determine the real cleaner life on the plating line. Making these analyses each day (or on some routine basis) will emphasize the cleaner’s trend in the process line. Then, informed decisions can best be made about the real cleaner life in each case.
Method I: Total Alkalinity/Free Alkalinity Ratio
- Obtain a sample of cleaner and allow to cool to room temperature.
- Pipette a 10 mL sample into an erlenmeyer flask and add 50 ml deionized water.
- Add three to five drops of phenolphthalein indicator.
- Pipette the pink solution with 0.5 N acid to a clear endpoint.
- Record the number of mLs of acid as A.
- Pipette a second 10 mL sample into an erlenmeyer flask and add 50 ml deionized water.
- Add three to five drops of methyl orange indicator.
- Pipette the orange solution with 0.5 N acid to a pink endpoint.
- Record the number of mls of acid as B.
Calculation: B/A = Total Alkalinity/Free Alkalinity Ratio
This determination should be made on both a brand new solution and a solution that has been used to the point that the cleaning quality is no longer acceptable. The ratio will be much higher on the ‘old’ cleaner, and this number (ratio) may now be used as an indicator to determine the solution life. It is important to note that the results of this method will change due to water quality, solution dragout and soil type, and by itself is not recommended to be the lone determining factor. Method III is more comprehensive.
Method II: Oil Split. Determine how much emulsified oil is being held by a particular cleaner.
- Obtain a sample of the cleaner and allow to cool to room temperature.
- Add 70 mL of cleaner to be tested to a 100 mL graduated cylinder.
- Carefully add 30 ml concentrated sulfuric acid to the graduated cylinder.
- Allow to cool/settle.
- Measure the ml amount of oil that floats to the surface.
This determination should be made on a solution that has been used to the point that the cleaning quality is no longer acceptable. Coventya has some specialized PRELIQ AB chemistries that can split emulsified oils from cleaning solutions to extend the solution life. Contact your local representative to determine if this approach could be right for your operation.
Method III: Three-Titration methodology is used successfully to track cleaner concentration and soil loading (contamination).
These titrations are effective for all alkaline cleaners that use phenolphthalein to maintain concentration. Generally, the cleaner sample size is 10 mL and titrated against 1.0 N acid. These values may be different, but, as long as they are consistent for all titrations, they will be a good gauge for the solution life.
These titrations must be started with a fresh cleaner makeup or standard cleaner solution made up in the lab and continued until the bath is no longer functional. These values can then be used to approximate the disposal point for the next bath, provided the soils are relatively consistent. The three titrations are as follows:
- Free Caustic — Azo Violet Indicator; color change from violet to yellow. This titration will provide a value for free sodium and/or potassium hydroxide.
- Free Alkalinity — Phenolphthalein Indicator; color change from red/purple to clear. This titration is generally used to maintain concentration. It detects caustics as well as the alkalinity contributed by the other alkaline builders such as carbonate, silicates and phosphates.
- Total Alkalinity — Methyl Red Bromcresol Green Mixed Indicator (MRBCG); color change from green to red. This titration detects the alkalinity contributed by all the builders as well as the buildup of titratable contaminants such as soaps, amines and other ingredients removed by the cleaner.
Day-to-day testing of the initial bath using this approach should provide data that reveals a decrease in free caustic and an increase in total alkalinity. This should be plotted along with the reject count. Provided all else is constant, a point will be determined where the reject rate is deemed unacceptable. This can then be tied to a failure point for the total alkalinity level. The next cleaning tank solution can then be monitored until it approaches this failure level. It should be replaced before it reaches this point and before the rejects become unacceptable. This method overall has been shown to provide reliable results, provided the soils are generally consistent on the line and other factors on the line are held constant.
As an example, a metal finisher was experiencing difficulties with cleaning in the process line. A sample of the soak cleaner was analyzed using the three-indicators approach. For comparative purposes, a lab batch of the same cleaner was made up at the same phenolphthalein endpoint concentration when titrated against 1.0 Normal Acid for the production bath.
The following results were recorded:
|Titration Indicator||Lab Batch||Process Tank|
|Azo Violet Endpoint||2.8 mL||0.0 mL|
|Phenolphthalein||3.4 mL||3.4 mL|
|MRBCG Mixed Indicator||3.8 mL||6.0 mL|
What insight about the cleaning does this data reveal? Generally, the free alkalinity phenolphthalein titration will remain constant because it is being used to maintain concentration. As this titration decreases, fresh cleaner is added to maintain the concentration at the desired level. A primary problem with the phenolphthalein endpoint is represented by the fact that alkaline cleaners formulated with sodium hydroxide have an affinity to absorb carbon dioxide from the air over time and with use. The older the cleaner, the more carbon dioxide that has been absorbed. This absorption forms sodium carbonate which contributes to this titration value. The problem is that as Sodium hydroxide is used up or converted to carbonate, the phenolphthalein titration value stays the same or increases. This action signifies a loss in cleaning efficiency, while the titration shows there is enough cleaner to be effective. Carbonate is not a good builder for improving the cleaning efficiency.
The free caustic titration measured by Azo-Violet will generally decrease in spite of the cleaner additions. This occurs because a proportionally larger amount is being used to neutralize fatty acids and react with other organic and inorganic soils. An Azo-Violet titration value much less than the lab batch value indicates that the free-sodium hydroxide formulated into the cleaner has been consumed, which is often the case. Here, the value is zero which represents no available alkalinity for improving cleaning efficiency. Since many soils are more easily removed when free-sodium hydroxide is present, a significant decrease in detergency with a resulting decrease in cleaning ability can be expected when this value is lower than optimum.
A high MRBCG-mixed indicator titration (measuring total alkalinity) is indicative of high levels of contamination from ingredients of soils that can also contribute to this titration. Examples of these types of soils are soaps, fatty acids, fatty oils and amines. Even though the insoluble soils are being removed from the work, some soluble portions of these soils are accumulating in the cleaner and making it difficult for the cleaner to perform its desired function. As the contaminants build up in solution, a point will be reached that will cause the cleaner to fail. An arbitrary point appears to be the point where this titration doubles from its original value. Naturally, some soils are easy to remove and the cleaner will function at a higher level of contamination, while other soils are more difficult to remove and the cleaner will cease to function at a value less than the arbitrary point. A reduction in detergency is usually the result of too high a value.
Method IV: Quantity of Additions
- Record the amount of the cleaner concentrate used at makeup.
- Keep a record of all cleaner additions made during operation.
- When the total additions equal the original makeup amount, it is time to consider replacing the cleaner.
- At this point, it may be beneficial to compare data from Methods II or III as there could be some other techniques to enhance performance.
Greg Terrell is director of business development at Coventya. Visit coventya.com
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